The present application relates to welding control systems. More particularly, it relates to welding control systems that can be produced, operated and maintained at a low cost.
Welding apparatus are frequently utilized together with robots, workpiece transferring systems, and workpiece positioning jigs to automate the welding process. In such cases, it is necessary to synchronize the operation of, for instance, the robot and the welding apparatus. Normally, when the workpiece has been moved by the workpiece transferring system to a prescribed position and/or the workpiece positioning jig has reached at a prescribed position in which welding can be performed, a signal to start welding is sent to the welding control apparatus. Hereinafter, the apparatus that sends the signal to start welding to the welding apparatus will be called the xe2x80x9cupper control apparatus.xe2x80x9d
The optimum welding conditions, such as the magnitude of the welding current, the time variation of the current magnitude, the duration of the current flow, and the pressure applied to the workpiece by the pair of welding guns and other welding parameters, will vary. The welding conditions depend, for example, on the type of material that is being welded, its thickness, surface treatment and welding position. Therefore, a plurality of welding sequence data, which correspond to the various types of welding operations, are stored in the welding apparatus. After accessing the specific welding sequence data that correspond to the type of welding to be performed, the prescribed welding process is initiated.
As shown in FIG. 1, a known welding control system includes upper control apparatus 102, welding control apparatus 122, and a set of cables 100 connecting the two apparatus.
The upper control apparatus 102 controls the robot, workpiece transferring system, positioning jig for the workpiece, and the time to start the welding. Upper control apparatus 102 comprises CPU 106, memory unit 108, and input/output interface (I/O) 110. A teaching apparatus 104 for the upper control apparatus 102 is connected to the upper control apparatus 102. The program and data necessary for the upper control apparatus 102 to control the robot, workpiece transferring system, and workpiece positioning jig are sent to the upper control apparatus 102 from the teaching apparatus 104. Timing data for the welding control apparatus 122 to start the welding, and data instructing the type of welding to be performed at the prescribed time, are also sent to the upper control apparatus 102 from the teaching apparatus 104. These instruction data are stored in the memory unit 108.
The welding control apparatus 122 controls the welding apparatus by controlling the welding transformer 136 and a set of valves 138 that controls the opening and closing of a pair of welding guns (not shown). The welding control apparatus 122 comprises CPU 126, memory unit 128, No. 1 I/O 124, No. 2 I/O 130, and a switching element 132. The switching element 132 is placed between the welding power supply 134 and welding transformer 136 and controls the effective welding current by intermittently turning on and off the connection of the welding power supply 134 and welding transformer 136. The welding transformer supplies current to the pair of welding guns.
A teaching apparatus 105 is provided for the welding control apparatus and is connected to the welding control apparatus 122. The pertinent data necessary for the control of the welding operation is transmitted to the welding control apparatus 122 from the teaching apparatus 105, and stored in memory unit 128. The welding sequence data, which is transmitted from the teaching apparatus 105, is stored in memory unit 128 of the welding control apparatus 122.
In order to achieve satisfactory welding results, various welding conditions, such as the magnitude of the welding current, the time variation of the current magnitude, the duration of the current flow, and the pressure applied to the workpiece by the pair of welding guns and other welding parameters, must be adjusted to optimum values. However, these optimum values differ for different types of welding conditions. For example, a lower welding current is preferred when welding thin iron plates as compared to thick iron plates, because the heat dissipated to the area surrounding the welding point is less. Similarly, a lower welding current is preferred when welding the comer of iron plates as compared to the center of iron plates, because the heat dissipated to the area surrounding the welding point is less. Thus, welding control apparatus 122 must be capable of welding using optimum conditions that are suitable for each different type of welding environment, such as thick iron plates, thin iron plates and welding the comers or the center of the plates. Therefore, teaching apparatus 105 is utilized to instruct the welding control apparatus 122 to use the appropriate set of data corresponding to the type of welding to be performed. The welding sequence data stored in memory unit 128 provides the data necessary to adjust the welding conditions to the optimum values for each type of welding. For example, welding sequence data 1 indicates the optimum welding conditions, such as the magnitude of the welding current, the time variation of the current magnitude, the duration of the current flow, and the pressure applied to the workpiece by the pair of welding guns and other welding parameters, for welding type 1, which may be for instance, comer welding of thin iron plates.
As described above, the upper control apparatus 102 is programmed to control the robots and other apparatus. At the appropriate time for the robot to start welding, upper control apparatus 102 outputs a signal to the welding control apparatus 122 to start the welding. The upper control apparatus 102 not only outputs the signal to start welding, but also outputs a signal to indicate the type of welding. Therefore, appropriate welding conditions for different types of welding can be provided.
At I/O 110 of the upper control apparatus 102, a number of separate output ports are provided to accommodate a corresponding number of welding types. Therefore, the signal indicating the welding type as well as the signal indicating the start of welding can be transmitted from the upper control apparatus 102 to the welding control apparatus 122. Similarly, a corresponding number of input ports are provided at I/O 124 of the welding control apparatus 122. Cable group 100 connects the corresponding ports. For example, when welding type 1 is to begin, the No. 1 port of I/O 110 is set high. This high signal is transmitted to the No. 1 input port of I/O 124 via one of the cables in the cable group 100. Then, instructions to start the welding using welding type 1 conditions are provided to the welding control apparatus 122.
Additionally, an output port is provided at I/O 124 so that a signal indicating the completion of the welding operation can be transmitted from the welding control apparatus 122 to the upper control apparatus 102. Similarly, an input port is provided at I/O port 110. The two ports are connected by cable 110 so that the welding complete signal can be transmitted from the welding control apparatus 122 to the upper control apparatus 102.
In this welding control system, a number of I/O ports corresponding to the number of welding types that can be performed by the welding control apparatus is required for each I/O port 110 and 124 of the upper control apparatus 102 and welding control apparatus 122. In addition, a number of cables corresponding to at least the number of welding types accommodated are required between the upper control apparatus 102 and the welding control apparatus 122. Furthermore, it is necessary to transmit a welding completion signal from the welding control apparatus 122 to the upper control apparatus 102. Consequently, the required number of ports and cables increases further.
There have been greater demands, in recent years, for production lines capable of producing many different types of products. Consequently, the number of different types of welding conditions has increased, and the number of necessary cables has increased, thereby increasing the labor costs that are necessary to maintain the cables. When two or more welding control apparatus are connected to the upper control apparatus, these issues become more problematic. For example, in an automobile assembly line, many welding apparatus operate simultaneously to assemble an automobile body. Therefore, many welding control apparatus are usually connected to the upper control apparatus.
In the known welding control system shown in FIG. 2, the system comprises s plurality of welding control apparatus (222A, 222B) connected to one upper control apparatus 202 via a set of cables 206. Because many cables are required to form the connections to the upper control apparatus 202, the wiring tasks become complex and the labor required to maintain the cable groups increases.
In order to reduce the number of cables required, a system shown in FIG. 3 has been developed. In the systems shown in FIG. 1 and FIG. 2, the number of cable groups equals the number of types of welding conditions plus one (one additional cable is required to transmit the welding complete signal) for each welding control apparatus. In the system shown in FIG. 3, the welding control apparatus 322A, 322B, 322C, etc. are connected to the upper control apparatus 302 via a field bus 350.
Field bus 350 is a system for connecting the upper control apparatus 302 in series with the welding control apparatus 322A, 322B, and 322C. It does not connect the upper control apparatus 302 and each welding control apparatus 322A, 322B, and 322C in parallel on a one-to-one basis as in FIG. 1 and FIG. 2.
In the system shown in FIG. 3, the welding type signal and the welding start signal are sent to the welding control apparatus 322A, 322B, and 322C via the field bus 350. At this time, in order to determine which welding control apparatus will receive the signal, a unique address is assigned to each welding control apparatus beforehand. Hereinafter, this unique address is called the xe2x80x9capparatus address.xe2x80x9d When it is time to start the welding operation, the upper control apparatus 302 outputs a particular apparatus address followed by a welding type signal to the field bus 350 in order to instruct the welding control apparatus having the same apparatus address to start welding. The data, which instructs each welding control apparatus to start a particular type of welding operation when the robot has reached a particular phase of its operation, are transmitted to the upper control apparatus 302 from the teaching apparatus 304, ahead of time.
The welding control apparatus receiving the apparatus address output from the field bus 350 inputs the welding type data following the apparatus address, and starts the welding control based on the corresponding welding sequence data.
The welding sequence data corresponding to the welding type are transmitted from the teaching apparatus ahead of time. As shown in FIG. 3, a teaching apparatus 305A supplies a plurality of welding sequences to the welding control apparatus A. Similarly, a teaching apparatus 305B supplies a plurality of welding sequences to the welding control apparatus B, and a teaching apparatus 305C supplies a plurality of welding sequences to the welding control apparatus C.
In the system shown in FIG. 3, the upper control apparatus 302 and the welding control apparatus 322A, 322B, and 322C are connected via field bus 350. I/O ports of the upper control apparatus and the welding control apparatus are not required to be connected in parallel on a one-to-one basis. Consequently, the number of required cables can be reduced significantly.
In addition, because this system utilizes the same teaching system shown in FIG. 1 and FIG. 2, the operators are likely to be familiar with the teaching function of the welding control apparatus.
However, in the system shown in FIG. 3, the welding sequence data is transmitted separately to each welding control apparatus. Consequently, each welding control apparatus requires a teaching apparatus, and instructions must be received from the corresponding teaching apparatus. This arrangement increases the cost of the system and makes the operation of the system cumbersome.
Another known welding control apparatus contains a program that detects and stores data concerning welding work in progress and under its control. For example, the magnitude of the welding current passed through the workpiece is detected and stored for each welding location. In this case, this type of monitoring system enables the analysis of the cause of welding defects discovered afterwards based on the recorded data.
It is desirable to have centralized management of monitored data when many welding control apparatus are used together. Consequently, a system taught by Japanese Patent No. 2514882 is shown in FIG. 4 in which a host computer 804 is connected to each welding control apparatus. The host computer 804 collects and stores the monitored data, and performs centralized monitoring. In this system, an upper control apparatus 800 and the centralized monitoring host computer 804 are connected to analyze the monitored data.
In the known system of FIG. 4, in which the host computer 804 is provided in addition to the upper control apparatus 800, each welding control apparatus A, B, and C is connected to the host computer 804 via a serial communication line 806. The host computer 804 accesses each welding control apparatus A, B, and C via the serial communication line 806 and extracts the monitored data.
The known system utilizing a field bus shown in FIG. 3 reduces the number of cables required to connect the upper control apparatus and the welding control apparatus over other known systems. However, in order to transmit the welding sequence data to the welding control apparatus, an exclusive teaching apparatus is needed for each welding control apparatus to transmit welding sequence data. This makes the operation of the system cumbersome.
Further, in the known system shown in FIG. 4, each welding control apparatus A, B, C, etc. must be connected to the upper control apparatus 800, and to the host computer 804, which requires extra wiring and increases the wiring costs. Additionally, the labor costs for maintenance and inspection of the wiring is high.
Therefore, it is one object of the present invention to teach welding control systems that overcome such problems in the art.
In one aspect of the present teachings, monitored data may be centrally managed simply by connecting each welding control apparatus A, B, C, etc. with the upper control apparatus 800.
In another aspect of the present teachings, the welding control apparatus may be programmed by the upper control apparatus by outputting the address data of the welding control apparatus, the internal address of the welding control apparatus, and the welding sequence data from the upper control apparatus to the field bus.
In another aspect of the present teachings, a common teaching apparatus may program a plurality of welding control apparatus, thereby minimizing system requirements and simplifying operation.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.
The above and other preferred features of the invention, including various novel details of implementation and combination of elements will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular methods and circuits embodying the invention are shown by way of illustration only and not as limitations of the invention. As will be understood by those skilled in the art, the principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.